trusty (3) sched_setscheduler.3posix.gz
NAME
sched_setscheduler - set scheduling policy and parameters (REALTIME)
SYNOPSIS
#include <sched.h> int sched_setscheduler(pid_t pid, int policy, const struct sched_param *param);
DESCRIPTION
The sched_setscheduler() function shall set the scheduling policy and scheduling parameters of the
process specified by pid to policy and the parameters specified in the sched_param structure pointed to
by param, respectively. The value of the sched_priority member in the sched_param structure shall be any
integer within the inclusive priority range for the scheduling policy specified by policy. If the value
of pid is negative, the behavior of the sched_setscheduler() function is unspecified.
The possible values for the policy parameter are defined in the <sched.h> header.
If a process specified by pid exists, and if the calling process has permission, the scheduling policy
and scheduling parameters shall be set for the process whose process ID is equal to pid.
If pid is zero, the scheduling policy and scheduling parameters shall be set for the calling process.
The conditions under which one process has the appropriate privilege to change the scheduling parameters
of another process are implementation-defined.
Implementations may require that the requesting process have permission to set its own scheduling
parameters or those of another process. Additionally, implementation-defined restrictions may apply as to
the appropriate privileges required to set a process' own scheduling policy, or another process'
scheduling policy, to a particular value.
The sched_setscheduler() function shall be considered successful if it succeeds in setting the scheduling
policy and scheduling parameters of the process specified by pid to the values specified by policy and
the structure pointed to by param, respectively.
If the scheduling policy specified by policy is SCHED_SPORADIC, the value specified by the
sched_ss_low_priority member of the param argument shall be any integer within the inclusive priority
range for the sporadic server policy. The sched_ss_repl_period and sched_ss_init_budget members of the
param argument shall represent the time parameters used by the sporadic server scheduling policy for the
target process. The sched_ss_max_repl member of the param argument shall represent the maximum number of
replenishments that are allowed to be pending simultaneously for the process scheduled under this
scheduling policy.
The specified sched_ss_repl_period shall be greater than or equal to the specified sched_ss_init_budget
for the function to succeed; if it is not, then the function shall fail.
The value of sched_ss_max_repl shall be within the inclusive range [1, {SS_REPL_MAX}] for the function to
succeed; if not, the function shall fail.
If the scheduling policy specified by policy is either SCHED_FIFO or SCHED_RR, the sched_ss_low_priority,
sched_ss_repl_period, and sched_ss_init_budget members of the param argument shall have no effect on the
scheduling behavior.
The effect of this function on individual threads is dependent on the scheduling contention scope of the
threads:
* For threads with system scheduling contention scope, these functions shall have no effect on their
scheduling.
* For threads with process scheduling contention scope, the threads' scheduling policy and associated
parameters shall not be affected. However, the scheduling of these threads with respect to threads in
other processes may be dependent on the scheduling parameters of their process, which are governed
using these functions.
If an implementation supports a two-level scheduling model in which library threads are multiplexed on
top of several kernel-scheduled entities, then the underlying kernel-scheduled entities for the system
contention scope threads shall not be affected by these functions.
The underlying kernel-scheduled entities for the process contention scope threads shall have their
scheduling policy and associated scheduling parameters changed to the values specified in policy and
param, respectively. Kernel-scheduled entities for use by process contention scope threads that are
created after this call completes shall inherit their scheduling policy and associated scheduling
parameters from the process.
This function is not atomic with respect to other threads in the process. Threads may continue to
execute while this function call is in the process of changing the scheduling policy and associated
scheduling parameters for the underlying kernel-scheduled entities used by the process contention scope
threads.
RETURN VALUE
Upon successful completion, the function shall return the former scheduling policy of the specified
process. If the sched_setscheduler() function fails to complete successfully, the policy and scheduling
parameters shall remain unchanged, and the function shall return a value of -1 and set errno to indicate
the error.
ERRORS
The sched_setscheduler() function shall fail if:
EINVAL The value of the policy parameter is invalid, or one or more of the parameters contained in param
is outside the valid range for the specified scheduling policy.
EPERM The requesting process does not have permission to set either or both of the scheduling parameters
or the scheduling policy of the specified process.
ESRCH No process can be found corresponding to that specified by pid.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
sched_getparam() , sched_getscheduler() , sched_setparam() , the Base Definitions volume of
IEEE Std 1003.1-2001, <sched.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The
original Standard can be obtained online at http://www.opengroup.org/unix/online.html .